1. Field of the Invention
The invention is related generally to apparatus for compensating for temperature-induced structural size variations occurring in machine components during a manufacturing process. More particularly, the invention relates to a temperature compensation apparatus utilized in gear production equipment.
2. Description of the Prior Art
Many manufacturing processes are affected by ambient or operational temperature changes occurring during manufacture. Gear production processes utilizing machinery for producing gears by any one of several methods are particularly sensitive to temperature variations occurring during the manufacturing process. Gear production equipment is generally sensitive to center distance, i.e. the distance between the center of the gear being produced and the center of the tool cutting the gear. Thermal expansion and contraction of various components of gear production equipment causes varying center distance and consequent variations in the gear being produced.
One type of gear production machinery susceptible to such temperature variations is the hydromechanical gear shaping machine as shown in U.S. Pat. Nos. 4,125,056, 4,136,302 and 4,254,690 each of which has been assigned to the assignee of the present invention and is incorporated by reference herein. Such gear shapers are referred to herein as a means of describing the invention although it will be understood that the invention is suitable for other gear production equipment.
A gear shaper such as shown in the aforementioned patents produces gears from a workpiece mounted on a rotating worktable. A cutter is mounted on a spindle whose axis is substantially parallel to the worktable axis. Moving or feeding the cutter spindle relative to the workpiece in a predetermined manner while reciprocating the spindle and rotating the worktable causes the cutter to shape a gear. It is apparent that the center distance between the workpiece and the cutter must be accurately controlled in order to produce the desired shape.
Hydromechanical gear shapers use closed loop servo systems to provide for extremely accurate positioning of the center distance between the centerline of a gear shaper cutter spindle and the centerline of the workpiece through the use of digital or analog feedback devices sensing various parameters of the machine structure. However, such feedback devices are insensitive to temperature dependent expansion and contraction of components of the machine. This creates size changes in the gears being produced, which changes are a function of the operating temperature of the machine components. It has been found that temperature variations during the production of any particular gear, may result in size variations of finished gears of as much as 0.003 inches. This part-size variation is most noticeable in large gears requiring several hours to produce. In extreme circumstances a spiral cut is caused and a step occurs in the gear's circumference. The defective gears so produced must either be re-cut to different specifications or discarded.
Temperature changes may be induced by any number of things. Obviously, ambient temperature changes occurring between the beginning and end of a particular work shift or cycle are significant. Additionally, the mere operation of the gear shaper causes its various components to heat up during the operational cycle. Furthermore, various operating conditions, such as the amount and type of coolant, whether or not the operation is continuous over a work day, types of materials being cut, size of the workpiece, etc., all contribute to operational temperature variations.
Production accuracy of prior art machines is enhanced with limited success by controlling these various temperature inducing parameters to maintain temperature stability. For example, these machines could be operated in temperature controlled, air conditioned environments under constant operating conditions or could be continuously operated 24 hours a day. These various methods used to ensure accurate production are quite costly and, as a practical matter, prior art gear shapers are usually run through a "warm up" period which generally requires considerable time to enable the machine to reach temperature equilibrium. This equilibrium must then be maintained by attempting to operate the machine at a constant cutting rate. Usually, if operating parameters of feed and speed are changed, the heat generated by rotating or reciprocating machine members increases or decreases establishing, after a period of time, a new equilibrium at a different structural temperature which results in an associated size change of the workpiece. Prior art machines are also affected by the fact that various critical machine components, due to their masses and heat dissipation properties, not only reach equilibrium at different temperatures but also over different time spans so that their combined effect on gear size could cause an initial center distance reduction and a subsequent increase as different components of the machine structure change their temperature.
Even if the aforementioned parameters may be controlled, changes in ambient air temperature over a full day of operation, or the temperature of the cutting fluids used will cause additional size changes even at contant cutting speeds and feeds.
It is accordingly an object of this invention to produce an apparatus to compensate for temperature induced structural variations occurring during a manufacturing process. It is a further object of this invention to produce an apparatus for automatically compensating for temperature induced structural variations of gear production equipment.